This invention relates to plastic tubing, and in particular an apparatus and method for joining ends of melt processable plastic tubing together to form a beadless weldment.
Tubing assembly is generally achieved by the use of fittings and fixtures. This is acceptable for many applications, however, there are drawbacks to this form of assembly. When fittings are used to join two tubes together, for example, the interior surface of the assembled tubing is often left with spaces or gaps between the ends of the tubes and the fittings or the ends of the tubes opposing each other. In other words, the interior surface is not smooth. One problem is that particulates may accumulate or accrete in the gaps or spaces and serve as a source of chemical contamination for fluids passing thereby. The accumulated or accreted particulates may also break away from the gap to create a source of physical or mechanical contamination. Another problem with the use of fittings and fixtures is that volatile components of the bonding materials used in assembly may leach out and become a source of contamination. Additionally, the bond itself may adversely react with fluids transported in the tubes and/or may become unduly embrittled or weakened. Another problem that arises is that the uneven interior surface may become a source of unwanted turbulence and flow resistance for fluid passing thereby. Such fittings are, of course, subject to leakage.
These drawbacks are of particular importance in industries where high levels of purity and cleanliness are necessary as in semi-conductor processing or required by law as in food processing.
These problems are alleviated by joining tubes to each other without the use of fittings. This is typically accomplished by welding, fusing, gluing or otherwise joining the tubes together. Concurrent with this shift in methods of assembly is the preferential use of plastic pipes and tubing of material such as perfluoroalkoxy (PFA) over the more traditional stainless steel which is, among other things, relatively hard to fabricate, expensive, and subject to corrosion.
Various means have been known for welding together the ends of thermoplastic pipes, see for example U.S. Pat. No. 4,929,293 to Oscar, which utilizes the placement of an infrared heating plated in between and confronting the tubular end pieces to be joined. The infrared heating plate is removed and the tube joints are then engaged together to create the weld.
With this and other types of assembly, many of the disadvantages of using fittings are reduced or eliminated, resulting in less contamination, increased flow efficiencies and greater overall strength.
There is a problem with these types of assembly, however, in that the seam or junction between tube ends is often not coincident with the interior surface of the conjoined tubes. That is, there may be a bead at the seam or junction which protrudes radially inwardly relative to the interior surface of the conjoined tube and/or there may be a bead at the seam or junction which protrudes radially outwardly relative to the interior surface of the conjoined tube. These beads, though relatively small, can also lead to contamination, turbulence and resistance as discussed above.
Various devices have been developed to reduce or eliminate the radially inwardly protruding seam or junction. These devices generally involve placing a temporary form or insert in the interior of tube ends to be joined, joining the tube ends, and then removing the temporary insert or form. The temporary inserts or forms are usually positioned coincident with the interior surfaces and ends of the tubes to be conjoined so that any gaps therebetween are spanned by the insert. The inserts or forms are of sufficient strength to resist compressive forces incurred during the conjoining process. Some of the devices which have been developed include inflatable bladders, elastically deformable expanding plugs, soluble plugs, frangible plugs, and mechanically adjustable mandrels (see, for example U.S. Pat. No. 5,484,506 to DuPont et al. and U.S. Pat. No. 5,037,500 to Hilpert both of which disclose the use of radially expandable internal mandrels to allow engagement of the interior surface of the tubular end portions to be joined and then allow the mandrel to be radially retracted and removed from the tubing). These devices have their drawbacks, however.
The inflatable bladder insert, for example, is usually longitudinally shaped and is designed to exert a radially extending outward force as it is pressurized. The bladder is not functional as an insert per-se and requires a source of working fluid, a delivery system, and a control system to enable the bladder to be filled and emptied to predetermined pressures. The requirement of such systems not only increases the complexity of the device, it necessarily restricts the number of locations where the device may be operated. Moreover, the bladder may be accidently punctured and lose its ability to be pressurized.
The elastically deformable expanding plugs do not suffer from the infirmities of the bladder, however, they do require specialized tools and fixtures to compress and elastically and radially deform a plug (or plugs) to an operable, supportive position within the tube ends. If the fixture breaks, or the interface between the specialized tools and the fixture becomes damaged, the plug will be inoperable.
Soluble and frangible plugs are designed to be used once and must be destroyed in order to be removed. That is, removal is accomplished by absorption and/or erosion by a suitable fluid medium or by fracturing, respectively. While these types of plugs are simple to use and do not require specialized tools or fixtures, they have their drawbacks in that they are relatively brittle and may break due to mishandling or accident prior to use. And, they may become sources of contamination due to incomplete and/or ineffective removal after use and it can be time consuming to remove such plugs.
Mechanically adjustable mandrels are relatively complicated to fabricate and assemble. They usually comprises a plurality of radially movable parts which are interconnected to each other by spring or similar retaining elements. Their construction permits variety of different tube sizes to be conjoined. Thus, one adjustable mandrel can replace a set of non-adjustable mandrels. This advantage is also a disadvantage in that the adjustable mandrel can come out of adjustment, or the radial parts may become misaligned or lost. Moreover, because they must be adjusted each time they are used on different sized tubes, they create significant down time.
There is a need for a tubing insert or form which is simple to manufacture, easy to install and remove, may be used at a variety of applications at a variety of work locations, and which may be used more than once.
The present invention solves the drawbacks inherent to the above-mentioned inserts or forms by eliminating the need for extraneous mechanisms, systems, and tools; by eliminating the need to exert stresses on components of the forms during use; by eliminating possible contamination due to incomplete or ineffective removal; and, by minimizing the number of parts and simplifying the operation of the insert.
Generally, the insert of the present invention comprises two portions which are operatively connected to, and longitudinally movable with respect to each other between two different configurations. In the first configuration, the insert is in supporting contact with the interior surfaces of tubing end portions as they are being conjoined, thus facilitating the formation of a beadless weldment. In the second configuration, the insert is manipulated out of supporting contact with the interior surfaces of tubing end portions to be conjoined, thus facilitating removal of the insert from the tubes.
More specifically, the insert comprises a first portion or component and a second portion or component. The first or core portion is generally cylindrical in shape and includes a nose, a tail, and a first circumferential support surface. The nose and the tail of the first core portion are streamlined to facilitate manipulation through non-linear sections of tubing. The preferred material of the first core portion is polyetheretherketone (PEEK) although other similar material may be used. The second or tubing contact portion is also generally cylindrical in shape and includes a skirt and an end wall which are arranged in a generally cup-shaped form. In view of the fact that the preferred plastic tubing material (perfluoroalkoxy (PFA)) used in the semi-conductor and food processing industries has a high melting temperature, the material selected for use in at least the skirt of the second tubing contact portion becomes important. The preferred material of the second tubing contact portion is a high temperature silicon No. 010-611 available from Robinson Rubber Mfg., New Hope, Mn. The insert is designed so that in the first conjoining configuration, the first core portion is substantially received within and supportingly contacts the skirt of the second tubing contact portion. When the insert is in the second removal configuration, the first core portion is out of supporting contact with the skirt of the second tubing contact portion. Put another way, the first portion or component and the second portion or component of the insert may be selectively assembled into a support structure to provide support for the tube end portions to be joined or disassembled into a non-support structure to facilitate removal of the insert from the tubing.
Portions of the first core portion and/or the second tubing contact portion of the insert may be provided with friction reducing material, such as polytetrafluoroethylene, to facilitate movement between the first and second configurations and subsequent removal of the insert from the tubing. Such friction reducing material may be integral with the insert portions, or take the form of an additional layer of material, or be applied to predetermined surfaces in predetermined quantities.
In an alternative embodiment, the second tubing contact portion may be used as a stand alone insert. It is envisioned that the application for this embodiment would be useful in situations where tubing is of thin wall construction, and/or is relatively small in diameter.
In another alternative embodiment, the first core portion may be manipulated between a relatively compact form and a relatively expanded form. As the insert is moved from the first conjoining configuration to the second removal configuration, the first core portion and the second tubing contact portion move longitudinally with respect to each other as in the preferred embodiment.
In yet another alternative embodiment, the second tubing contact portion includes an additional coaxial segment which is configured to receive the first core portion as the insert moves from the first conjoining configuration to the second removal configuration.
Although not shown, it is envisioned that the second tubing contact portion may alternatively be formed as a strip of heat-resistant material operatively connected to the first portion and which has been wound about the support surface of the first portion to a suitable thickness. As the first portion is withdrawn, the end of the second portion starts to unwind, thus facilitating removal of the form. It is also envisioned that such a strip may be used over the second tubing contact portion of the preferred embodiment as an insulator, thus extending the working temperature range of the insert.
An object of the preferred embodiment of the invention is to simplify construction of an insert for use in conjoining plastic tubular end portions to form a beadless weldment.
An advantage of the preferred embodiment is that the insert is easy to use.
A feature of the preferred embodiment of the invention is that the first core portion and the second tubing contact portion of the insert are slidingly movable with respect to each other in a longitudinal direction.
Another feature of the preferred embodiment of the invention is that the first core portion and the second tubing contact portion are movable between a first conjoining configuration where the first core portion is in supporting contact with the second tubing contact portion, and a second removal configuration where the first core portion is not in supporting contact with the second tubing contact portion.
Yet another feature of the preferred embodiment of the invention is that one of the portions of the insert is everted when the insert is moved from the first conjoining configuration to the second removal configuration.
A further significant feature of a preferred embodiment of the invention is that the insert can be manipulated through corners such as elbows and xe2x80x9cT""s.xe2x80x9d
Additional objects, advantages, and features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.